The role of PKM2 in cancer has been scrutinised and reviewed by many authors, and it is clear that the expression of this PK isoform promotes cell growth and proliferation.35–39 Among the advantages of expression of PKM2 is the favouring of the Warburg effect over oxidation40 through promoting the expression of HIF-1α.39 Indeed, 5-HT promotes the expression of HIF-1α, as will be further shown and discussed. This evidence concerns the gene HIF1A and cancer.